To adjust the geometry of a display such as a CRT monitor for a computer system, it is desirable to produce on the display a symmetric pattern such as a rectilinear hatch or grid. The effect of geometric adjustments made to the display can easily be seen by their effect on the symmetry of the grid.
Conventionally, in order to display a grid it is necessary to use an external display generator to produce the necessary pattern. Such an external display generator is expensive and is typically used only by the manufacturers of displays such as monitors.
Although it would be desirable to produce the necessary display pattern internally, so avoiding the need for an external display generator and allowing both the manufacturer and any subsequent user of the display to utilize the pattern in adjustment of the display, such internal pattern production presents practical difficulty. If the display pattern is to be produced on a 1,280 by 1,024 pixel screen, the necessary monochrome screen image will require 160 kilobytes of memory for storage. Such a large of amount of memory adds considerably to the cost of an integrated circuit component, such as an on-screen display (OSD) device, which could conveniently be utilized for storage and generation of the image. Also, if the display pattern is to be produced in a variety of display modes with different pixel sizes, either a number of different images must be stored (e.g., one for each different pixel size display mode) further compounding the storage problem, or some mechanism must be found for converting a stored image for one pixel size display mode into a different image for a different pixel size display mode.
It is an object of this invention to provide a circuit for use in generating a line pattern display in which the above disadvantages are alleviated.